The objective of this study is to clinically evaluate Tc99m-Sn- pyrophosphate as a bone imaging agent. Another radiopharmaceutical, Co57 bleomycin was also evaluated to determine its sensitivity for numerous malignant lesions. The Tc99m-Sn-pyrophosphate appears to be a good diagnostic tool for bone imaging because of the high bone uptake, low soft tissue uptake, and satisfactory quality control systems which can indicate radiochemical purity. In addition to localization in the bone, the Tc99m-Sn-pyrophosphate also showed localization in extraosseous tissue. Bleomycin has undergone extensive investigation as a cancer chemotherapeutic agent. Previous studies in our laboratory demonstrated significant accumulation of labeled bleomycin in transplanted experimental tumors in mice. We have evaluated Co57 labeled bleomycin as a tumor scanning agent in 47 patients with malignant lesions and 6 patients with benign lesions. In terms of diagnostic sensitivity, labeled bleomycin was found to be superior to the often used tumor imaging agent Ga67 citrate.